The glutathione (GSH) redox system provides important intracellular protection against oxidant stress injury. All of the studies on the cellular effects of oxidants on the GSH redox cycle have been done in eucaryotes. Since one goal of toxicological research is the use of fewer animals, a procaryotic model to study the effects of oxidants on the GSH synthesis and redox cycle may lessen dependence on animal models for similar studies. GSH synthesis and degradation proceeds by common pathways in both systems. The enzymes responsible for the GSH redox cycle appear to be similar in function in pro-and eucaryotes, and, in the case of GSH reductase, show close homology. GSH-peroxidase is widely thought to be restricted to eucaryotes yet we have found a GSH-dependent peroxidase in E. coli. A number of the effects of oxidants on GSH observed in eucaryotes have also been observed in E. coli. These are described in the Preliminary Results section in this proposal. We propose to show that E. coli may model the effect of oxidant stress on eucaryotic systems. This will be accomplished as follows: 1. Confirm that the components of the GSH redox system are similar between eucaryotes and E. coli. Isolate and compare the GSH-dependent peroxidase to the one found in eucaryotes. 2. Show that the effected of oxidant stress on the GSH redox system are similar in eucaryotes and E. coli. 3. Demonstrate that, following oxidant stress, the effect of decreasing or increasing intracellular GSH are qualitatively similar between procaryotes and eucaryotes. 4. Show that effect of oxidant stress of GSH synthesis in both systems are similar; thus confirming the validity of the model.